From linear response theory [1]}, we can compute the response of a given observable \(B\)  to an external perturbation of the form \(\Delta \mathcal {H}=A(x_i)F_{0}=\mathcal {H}_{\text{ext}}\)  as
\({ <B>=L_{AB}F_0=\left[ \frac{1}{k_BT} \int _0^{\infty }<B(t) \dot{A}(0)> dt\right]F_0\;.}\) 
